Results 1 to 4 of 4

Math Help - Petagons

  1. #1
    Member Rimas's Avatar
    Joined
    Sep 2006
    From
    West Philly
    Posts
    86

    Petagons

    A diagnal of a polygon is a degment joining the two nonconecutive vertcies of the polygon.How many dianals does a regular octagon have?
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Senior Member OReilly's Avatar
    Joined
    Mar 2006
    Posts
    340
    Quote Originally Posted by Rimas View Post
    A diagonal of a polygon is a segment joining the two nonconsecutive vertcies of the polygon.How many dianals does a regular octagon have?
    It has 20 diagonals.

    Formula is:
    D_8  = \frac{{8(8 - 3)}}{2} = \frac{{40}}{2} = 20
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Senior Member
    Joined
    Apr 2006
    Posts
    401
    Quote Originally Posted by Rimas View Post
    A diagnal of a polygon is a degment joining the two nonconecutive vertcies of the polygon.How many dianals does a regular octagon have?
    We know that the octagon has exactly 8 vertices. We are then able to create 5 diagonals from a given vertex.

    8*5 = 40; however, there are some repeats. Each diagonal is counted twice since there are 2 points to each diagonal. Thus, 40/2 = 20 is the number of diagonals in a regular octagon.
    Follow Math Help Forum on Facebook and Google+

  4. #4
    Senior Member OReilly's Avatar
    Joined
    Mar 2006
    Posts
    340
    General formula for counting number of diagonals for any polygon is:

    D_n  = \frac{{n(n - 3)}}{2}

    where n is number of sides.
    Follow Math Help Forum on Facebook and Google+

Search Tags


/mathhelpforum @mathhelpforum